We will utilize a novel recombination-based assay (RBA) to select genes and thereby perform a time and tissue analysis of transcription for expressed sequences on chromosome 19. Reversal of this selection, counterselection, will be performed to yield the gene of interest and allow rapid DNA sequencing of the gene. Rapid performance of these steps will permit us to append a "genic" initiative onto the "genomic" initiative. We have elaborated novel bacterial strains, plasmids and schemes for the RBA. The bacterial strains include DM21,, a dnaB amber line that enables us to select for phages that share homology with a defined sequence; pMAD3, a supF plasmid without homology to ColE1 that allows us to select without background for phages - that share homology to a sequence cloned in pMAD3; PCR counterselection, that permits us to select efficiently against supF, thereby allowing us to isolate rapidly a desired sequence selected by recombination. This methodology will be applied in tandem with efforts at Lawrence Livermore to isolate and catalogue expressed sequences on chromosome 19. Regardless of whether this or other technology is utilized to identify transcribed sequences, the RBA will be employed to identify the time and tissue of transcription in an efficient manner.